34 results for Alloway, Brent

  • The role of Egmont-sourced tephra in evaluating the paleoclimatic correspondence between the bio- and soil-stratigraphic records of central Taranaki, New Zealand

    Alloway, Brent; McGlone, MS; Neall, VE; Vucetich, CG (1992)

    Journal article
    The University of Auckland Library

    On the lower eastern flanks of Egmont Volcano, western North Island, New Zealand, several Egmont-sourced tephras have been correlated to a radiocarbon dated peat site that provides a late last-glacial to early post-glacial record of vegetation and climate change in central Taranaki. The pollen spectra at this site indicates a mosaic of grassland-shrubland and Prumnopitys taxifolia-dominant forest at ca. 13,100 BP and suggests a climate cooler and drier than at present. The ominance of tall podocarp forest by ca. 12,900 BP suggests that climatic amelioration was rapid towards the end of the last glacial period. Initially this forest was dominated by Prumnopitys taxifolia but at ca. 11,000 BP was succeeded by Dacrydium cupressinum indicating a steady shift to warmer and moister climate. Tephra interbedded with peat allows precise chrono-correlation into the Andisol-forming environment. The rapidity of climatic amelioration identified from variations in Andisol morphology and mineralogy concurs with that indicated from pollen changes in the peat.

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  • Particle size analyses of Late Quaternary allophane-dominated andesitic deposits from New Zealand

    Alloway, Brent; Neall, VE; Vucetich, CG (1992)

    Journal article
    The University of Auckland Library

    On the western North Island, New Zealand, a Late Quaternary sequence of allophane-dominated cover-bed (Andisol) deposits have accumulated from intermittent accretion and rapid, subsequent weathering of aerially transported detritus of dominantly andesitic provenance. Particle size analyses of Andisol samples were attempted for textural classification and provenance studies. The hydrometer and sedigraph techniques were unsuccessful due to difficulties arising from the flocculation of short-range order clay and organic constituents (SROCO), which prevented complete particle dispersion. Neither acidic (HCl) nor alkaline (NH4OH or NaOH) solutions were effective in completely dispersing samples, so an alternative chemical procedure was devised. This alternative pretreatment involves the selective dissolution of Andisol SROCO constituents by 0.2 mol acid-oxalate reagent (pH 3.0???3.5), and has considerable potential in the determination of particle size, soil textural classification and provenance of allophane-dominated andesitic deposits.

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  • Climate of the last glaciation in New Zealand, based on aerosolic quartz influx in an andesitic terrain

    Alloway, Brent; Stewart, RB; Neall, VE; Vucetich, CG (1992-09)

    Journal article
    The University of Auckland Library

    On western North Island, New Zealand, a record of climatic change during the last glaciation is preserved in a terrestrial coverbed sequence of dominantly andesitic provenance. Here, a succession of five loess-like Andisol units postdates the global high sea-level stand of oxygen isotope substage 5e (<125,000 yr). Tephra erupted from western and central North Island allow precise chronological correlation of the loess-like units. Aerosolic quartz additions determined by quantitative X-ray diffraction (XRD) record two major peaks that correlate with oxygen isotope stages 2 and 4. The most likely source of quartz-rich dust at these times is the surrounding continental shelf, then exposed by low sea level; however, quartz of Australian provenance may also be represented. This study provides the first confirmation from the terrestrial New Zealand record that rates of atmospherically transported particles increase during glacial stages.

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  • A terrestrial record of Last Interglacial climate preserved by voluminous debris avalanche inundation in Taranaki, New Zealand

    Newnham, R; Alloway, Brent (2004-03)

    Journal article
    The University of Auckland Library

    At Airedale Reef, western North Island, New Zealand, a ca. 4???m thick volcanogenic debris avalanche deposit has facilitated the preservation of an enveloping sequence of peats with interbedded andesitic tephras spanning marine isotope (MIS) 5. The sequence closely overlies a wave-cut terrace correlated to MIS 5e and, in turn, is overlain by andic beds with tephra interbeds including the Rotoehu and Kawakawa tephras deposited during early MIS 3 and mid-MIS 2, respectively. Pollen analysis of the organic sequence shows a coherent pattern of fluctuating climate for the Last Interglacial???Last Glacial transition that corresponds with marine isotope stratigraphy and supports the contention that orbital variations were a primary factor in late Quaternary southern mid-latitude climate change. A five-stage subdivision of MIS 5 is clearly recognised, with marine isotope substage (MISS) 5b drier than MISS 5d, and the cooling transition from 5a to MIS 4 also may have been comparatively dry and characterised by natural fire, perhaps associated with volcanism. Several other examples of volcanic impact on vegetation and the landscape are evident. The Airedale Reef sequence exhibits strong similarities with fragmentary MIS 5 pollen records preserved elsewhere in New Zealand and enables the proxy record of southern mid-latitude climatic variability during the Last Interglacial???Glacial cycle to be extended.

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  • Vegetation and climate of Auckland, New Zealand, since ca. 32 000 cal. yr ago: support for an extended LGM

    Newnham, RM; Lowe, DJ; Giles, T; Alloway, Brent (2007-07)

    Journal article
    The University of Auckland Library

    Auckland occupies a climatically sensitive position close to a major biogeographic boundary in the southern mid-latitudes. A new pollen record from Kohuora maar crater, Auckland, displays vegetation and climatic changes for the past ca. 32???000 years. Of particular interest are the inferred climatic patterns for the first part of the interval, encompassing the Last Glacial Maximum (LGM). The Kohuora record corresponds closely with pollen records from other Auckland sites indicating that the patterns observed are at least regional in extent. It is also broadly consistent with a variety of palaeoenvironmental evidence from across New Zealand, including the glacial record from Westland, other palynological records from North Island, other palaeoecological records from the South Island, and aeolian quartz sequences from western North Island. These records show that glacial conditions prevailed across most, if not all, of New Zealand during the interval ca. 29???19???k cal.???yr???BP, longer and earlier than the LGM sensu stricto. We suggest that the term extended LGM (eLGM) may be more appropriate for the New Zealand region. Within this predominantly cold interval, the Auckland pollen records indicate a climatic amelioration for the interval ca. 26???24???k cal. yr BP, also consistent with other palaeocological data from Canterbury, that fall within a period of climate amelioration recognised between the first two eLGM glacial advances in Westland. We refer to this warming interval as the eLGM Interstadial. The ca. 27???k cal. yr BP Kawakawa/Oruanui tephra is instrumental in most of these inter-site comparisons and occurs after the first peak of eLGM cooling in a short-lived comparatively mild phase. A subsequent return to apparently colder climate in the Auckland records may indicate a volcanic cooling effect or, more likely, widespread landscape disturbance following this major eruption event. Strong correspondence between biotic responses, glacial fluctuations and aeolian quartz deposition linked to major shifts in strength and latitudinal extent of the southern westerlies suggest that both the eLGM and eLGM Interstadial may be more widely registered, at least across the Southern Ocean. Support for this assertion comes from parallel investigations in western and southernmost South America and isotopic and palaeoecological records from Southern Ocean marine cores. Recent reconstructions of the globally averaged ice-equivalent sea-level history are in line with this evidence from the Southern Hemisphere, suggesting that the eLGM may have a global registration. In light of these observations, we suggest a re-examination of the defined timing of the LGM along with renewed effort to establish climatic patterns during this period and understand their causes.

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  • Rates of deformation, uplift, and landscape development associated with active folding in the Waipara area of North Canterbury, New Zealand

    Nicol, A; Alloway, Brent; Tonkin, P (1994-12)

    Journal article
    The University of Auckland Library

    Analysis of the geometry and ages of faulted and tilted late Quaternary fluvial terraces and their associated cover beds provide evidence of active folding at three localities in the Waipara area of North Canterbury, New Zealand, Terrace survey data, the occurrence of the approximately 22.6-kyr-old Aokautere Ash, and examination of soil profiles indicate that folding has continued into the late Holocene but that the amounts and rates of deformation are locally variable. Rates of uplift in the Waipara area are compared with those derived from marine terraces preserved at the Pacific coast, east of the study area. Results indicate that rates of measurable deformation reach a maximum along the Waipara range front, where bedrock deformation is most intense and shortening rates of up to 5.57??0.69%/100 kyr occur. Across the coastal ranges the average rate of shortening is 0.8??0.4%/100 kyr, which corresponds with an absolute shortening rate of 1.4??0.6 m/kyr and represents only a small proportion of the predicted plate motion vector in this region. Uplift rates range from 0???1.83 m/kyr for a late last glacial fluvial terrace and from 1.36???2.16 m/kyr for three marine terraces. Fluvial and marine terrace uplift rates vary in accord with the geometries of the folds in bedrock, and the spatial pattern of uplift directly reflects fold growth. The structure contour pattern of folded surfaces provides a first approximation to the spatial pattern of uplift. Differential uplift due to folding accounts for up to approximately 55???75% of the total uplift and has produced folds with structural relief of about 1300 m (i.e., amplitudes of 600???700 m). These folds have formed over the last 0.8??0.4 m.y. since the onset of Quaternary deformation in the Waipara region.

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  • Correlation and characterisation of individual glass shards from tephra deposits using trace element laser ablation ICP-MS analyses: current status and future potential

    Pearce, NJG; Denton, JS; Perkins, WT; Westgate, JA; Alloway, Brent (2007-10)

    Journal article
    The University of Auckland Library

    Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a high spatial resolution analytical method which has been applied to the analysis of silicic tephras. With current instrumentation, around 30 trace elements can be determined from single glass shards as small as ??? 40?????m, separated from tephra deposits. As a result of element fractionation during the ablation process using a 266???nm laser, a relatively complex calibration strategy is required. Nonetheless, such a strategy gives analyses which are accurate (typically within ??5%) and have an analytical precision which varies from ??? ??2% at 100???ppm, to ??? ??15% at 1???ppm. Detection limits for elements used in correlation and discrimination studies are well below 1???ppm. Examples of the application of trace element analysis by LA-ICP-MS in tephra studies are presented from the USA, New Zealand and the Mediterranean. Improvements in instrumental sensitivity in recent years have the potential to lower detection limits and improve analytical precision, thus allowing the analysis of smaller glass shards from more distal tephras. Laser systems operating at shorter wavelengths (e.g. 193???nm) are now more widely available, and produce a much more controllable ablation in glasses than 266???nm lasers. Crater sizes of <10?????m are easily achieved, and at 193???nm many of the elemental fractionation issues which mar longer wavelengths are overcome. By coupling a short wavelength laser to a modern ICP-MS it should be possible to determine the trace element composition of glass shards as small as 20?????m and, providing sample preparation issues can be overcome, the determination of the more abundant trace elements in glass shards as small as 10?????m is within instrumental capabilities. This will make it possible to chemically fingerprint tephra deposits which are far from their sources, and will greatly extend the range over which geochemical correlation of tephras can be undertaken.

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  • The AUSTRALASIAN-INTIMATE project special volume

    Barrows, TT; Alloway, Brent; Reeves, J (2013-08-15)

    Journal article
    The University of Auckland Library

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  • Refuting the evidence for an earlier birth of the Taklimakan Desert

    Sun, J; Alloway, Brent; Fang, X; Windley, BF (2015-10-13)

    Journal article
    The University of Auckland Library

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  • An 18,000 year-long eruptive record from Volc??n Chait??n, northwestern Patagonia: Paleoenvironmental and hazard-assessment implications

    Alloway, Brent; Pearce, NJG; Moreno, PI; Villarosa, G; Jara, I; De Pol-Holz, R; Outes, V (2017-07-15)

    Journal article
    The University of Auckland Library

    The 2008 eruption of Volc??n Chait??n (VCha) in northwestern Patagonia was the first explosive rhyolitic eruption to have occurred within a century and provided an unprecedented scientific opportunity to examine all facets of the eruption ranging from magma rheology/ascent rates to ash-fall effects on biota and infrastructure. Up to very recently it was thought that the latest eruption prior to the 2008 event occurred c. 9750 cal. a BP. Although a number of researchers have recognised additional eruptive products, but their stratigraphy, age, and geochemical attributes have not been systematically described and/or recorded. In this study, we provide a detailed examination of andic cover-beds and tephra-bearing lake sequences located both proximally and distally to VCha, which record a series of hitherto unknown rhyolitic eruptive products and place all previous observations firmly within a coherent stratigraphic framework. Through major- and trace-element glass shard geochemistry we are able to confidently verify eruptive source. A total of 20 discrete tephra beds are recognised, with at least 10 having widespread areal distributions and/or depositional imprints broadly comparable to, or greater than, the 2008-tephra event. This record indicates that VCha has been continuously but intermittently active as far back as the end of the Last Glacial Maximum (c. 18,000 cal a BP) with two dominant, genetically related magma types and an intermediary ???mixed??? type. Before this the eruptive record has been largely obscured and/or erased by widespread Andean piedmont glaciation. However, based on the tempo of VCha activity over the last c. 18,000 years, older VCha eruptives can be anticipated to occur as well as future hazardous explosive events. The new eruptive inventory will ultimately be useful for correlating equivalent-aged sequences and refining long-term eruptive tempo as well as corresponding temporal changes in magmatic evolution.

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  • Revision of the marine chronology in the Wanganui Basin, New Zealand, based on the isothermal plateau fission-track dating of tephra horizons

    Alloway, Brent; Pillans, BJ; Sandhu, AS; Westgate, JA (1993-01)

    Journal article
    The University of Auckland Library

    The occurrence of tephra horizons in basins adjacent to volcanic arcs provide an excellent opportunity for establishing a reliable chronostratigraphic framework for detailed sedimentological studies. In this study, three widespread and stratigraphically important rhyolitic tephra horizons interbedded in Plio/Pleistocene strata of the Wanganui Basin, New Zealand, are dated by application of the isothermal plateau fission-track (ITPFT) technique to hydrated glass shards. All glass samples were corrected for annealing and consequently yield reliable ages. Rangitawa Tephra yielded statistically indistinguishable ages from three localities that are in excellent agreement with recently determined zircon fission-track age estimates of ca. 0.35 Ma. ITPFT ages of 1.05 ?? 0.05 and 1.63 ?? 0.15 Ma for Potaka Pumice and Pakihikura Pumice, respectively, are considerably older than previous FT estimates but consistent with new magnetostratigraphic data that places the Potaka within the Jaramillo Subchron, and Pakihikura within the Matuyama Chron between the Cobb Mountain and Olduvai Subchrons. Combining our fission-track ages with the magnetostratigraphy, the true age of sediments within the Wanganui Basin is found to be significantly underestimated. Sedimentation rates of between ca. 680-630 m/Ma from 1.63 Ma to 0.35 Ma are calculated in the eastern part of the basin and are much lower than those calculated using the previous FT chronology. This new ITPFT-age data demonstrates that the existing Plio/Pleistocene marine chronology in New Zealand will require age revision and has important implications when considering the evolution of several other sedimentary basins in southern North Island that contain the same ITPFT-dated tephra horizons.

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  • Silicic tephras in Pleistocene shallow???marine sediments of Wanganui Basin, New Zealand

    Pillans, B; Alloway, Brent; Naish, T; Westgate, J; Abbott, S; Palmer, A (2005-09-07)

    Journal article
    The University of Auckland Library

    Vitric???rich volcaniclastic horizons are important for correlation of glacio???eustatic sedimentary cycles, both within the well known shallow???marine record of Wanganui Basin, and other New Zealand terrestrial and deep marine records. They also record distal major rhyolitic eruptions from the Taupo (TVZ) and Coromandel (CVZ) Volcanic Zones that are lacking in proximal source areas. Twenty???eight volcaniclastic horizons are recognised in the Castlecliffian and late Nukumaruan strata of Wanganui Basin from glass shard major element geochemistry and stratigraphic position, and are dated using magnetostratigraphy, orbitally tuned cyclostratigraphy and isothermal plateau fission track (ITPFT) ages. The major named volcaniclastic horizons (with ITPFT and/or astronomical ages, respectively) are: Onepuhi (0.57 Ma), Kupe (0.63 ?? 0.08 Ma; 0.65 Ma), Kaukatea (0.86 ?? 0.08 Ma; 0.90 Ma), Potaka (1.00 ?? 0.03 Ma; 0.99 Ma), Rewa (1.20 ?? 0.14 Ma; 1.19 Ma), Mangapipi (1.51 ?? 0.16 Ma, 1.54 Ma), Ridge (1.56 Ma), Pakihikura (1.58 ?? 0.08 Ma; 1.58 Ma), Birdgrove (1.60 Ma), Mangahou (1.63 Ma), Maranoa (1.63 Ma), Ototoka (1.72 ?? 0.32 Ma; 1.64 Ma), Table Flat (1.71 ?? 0.12 Ma; 1.65 Ma), Vinegar Hill (1.75 ?? 0.20 Ma; 1.75 Ma), and Waipuru (1.79 ?? 0.15 Ma; 1.83 Ma). The ITPFT ages are consistent with the astronomically tuned Geomagnetic Polarity Timescale. Volcaniclastic horizons in Wanganui Basin have been emplaced through a variety of primary and secondary processes, including direct tephra???fall as well as transitional water supported mass flow through to hyperconcentrated flow. No gas supported flow deposits have yet been recognised. Only some horizons from Wanganui Basin can be chemically and chronologically linked to known TVZ eruptions, while others remain uncorrelated owing to proximal source area erosion and/or burial as well as vapour phase alteration and devitrification within near???source welded ignimbrites. Nevertheless, many volcaniclastic deposits in Wanganui Basin can be reliably correlated to distal sedimentary successions in Auckland Region, Hawke's Bay and in Ocean Drilling Program (ODP) cores 1123 and 1124, to the east of New Zealand. The orbitally tuned chronology for ODP cores, which is calibrated by numeric ages on tephras and magnetostratigraphy, enhances inter???regional correlation, providing an important framework for future pal???aeoenvironmental reconstructions.

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  • Demise of one volcanic zone and birth of another???A 12 m.y. marine record of major rhyolitic eruptions from New Zealand

    Carter, LC; Shane, Philip; Alloway, Brent; Hall, IR; Harris, SE; Westgate, JA (2003-06)

    Journal article
    The University of Auckland Library

    Ocean Drilling Program Sites 1123 and 1124 provide an unprecedented 12 m.y. record of major rhyolitic eruptions from the Coromandel and Taupo volcanic zones of New Zealand. Macroscopic tephras (n = 197) were dated using magnetostratigraphy, supplemented by geochemical correlation with subaerial tephra, isothermal plateau fission-track ages, and orbitally tuned stable isotope data. Eruptions began in the Coromandel volcanic zone ca. 12 Ma, ???1.6???1 m.y. earlier than previously known. Thereafter, volcanism was fairly continuous with a tempo and intensity that increased through the late Miocene???Pliocene and into the Quaternary, when the Taupo volcanic zone formed. The transition from the Coromandel to the Taupo zone, previously placed as ca. 4???2 Ma, was seamless, without obvious breaks or changes in ash composition. This well-dated history of long-lived and productive volcanism allows for more confident correlation with other circum-Pacific tephra records, thus helping confirm the occurrence of widespread coeval eruptions throughout the region.

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  • The Kerepehi Fault, Hauraki Rift, North Island, New Zealand: active fault characterisation and hazard

    Persaud, M; Villamor, P; Berryman, KR; Ries, W; Cousins, J; Litchfield, N; Alloway, Brent (2016)

    Journal article
    The University of Auckland Library

    The Kerepehi Fault is an active normal fault with a total onshore length of up to 80 km comprising six geometric/rupture segments, with four more offshore segments to the north. For the last 20????????2.5 ka the slip rate has been 0.08???0.4 mm a???1. Average fault rupture recurrence intervals are 5 ka or less on the central segments and 10 ka or more on low slip rate segments to the north and south. Characteristic earthquakes for a single segment rupture range from Mw 5.5 to 7.0, and up to Mw 7.2 or 7.4 in the unlikely event of rupture of all the onshore fault segments. Fault rupture would result in damage to unreinforced masonry buildings, chimneys and parapets in Auckland (45 km nearest distant). Very severe damage to buildings in towns within the Hauraki Plains without specific seismic design (those built before 1960) may pose a significant risk to life and livelihood.

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  • Onshore???offshore correlation of Pleistocene rhyolitic eruptions from New Zealand: implications for TVZ eruptive history and paleoenvironmental construction

    Alloway, Brent; Pillans, BJ; Carter, L; Naish, TR; Westgate, JA (2005-08)

    Journal article
    The University of Auckland Library

    Taupo Volcanic Zone (TVZ), in the North Island, New Zealand, is arguably the most active Quaternary rhyolitic system in the world. Numerous and widespread rhyolitic tephra layers, sourced from the TVZ, form valuable chronostratigraphic markers in onshore and offshore sedimentary sequences. In deep-sea cores from Ocean Drilling Program (ODP) Leg 181 Sites 1125, 1124, 1123 and 1122, located east of New Zealand, ca 100 tephra beds are recognised post-dating the Plio-Pleistocene boundary at 1.81 Ma. These tephras have been dated by a combination of magnetostratigraphy, orbitally tuned stable-isotope data and isothermal plateau fission track ages. The widespread occurrence of ash offshore to the east of New Zealand is favoured by the small size of New Zealand, the explosivity of the mainly plinian and ignimbritic eruptions and the prevailing westerly wind field. Although some tephras can be directly attributed to known TVZ eruptions, there are many more tephras represented within ODP-cores that have yet to be recognised in near-source on-land sequences. This is due to proximal source area erosion and/or deep burial as well as the adverse effect of vapour phase alteration and devitrification within near-source welded ignimbrites. Despite these difficulties, a number of key deep-sea tephras can be reliably correlated to equivalent-aged tephra exposed in uplifted marine back-arc successions of Wanganui Basin where an excellent chronology has been developed based on magnetostratigraphy, orbitally calibrated sedimentary cycles and isothermal plateau fission track ages on tephra. Significant Pleistocene tephra markers include: the Kawakawa, Omataroa, Rangitawa/Onepuhi, Kaukatea, Kidnappers-B, Potaka, Unit D/Ahuroa, Ongatiti, Rewa, Sub-Rewa, Pakihikura, Ototoka and Table Flat Tephras. Six other tephra layers are correlated between ODP-core sites but have yet to be recognised within onshore records. The identification of Pleistocene TVZ-sourced tephras within the ODP record, and their correlation to Wanganui Basin and other onshore sites is a significant advance as it provides: (1) an even more detailed history of the TVZ than can be currently achieved from the near-source record, (2) a high-resolution tephrochronologic framework for future onshore-offshore paleoenvironmental reconstructions, and (3) well-dated tephra beds correlated from the offshore ODP sites with astronomically tuned timescales provide an opportunity to critically evaluate the chronostratigraphic framework for onshore Plio-Pleistocene sedimentary sequences (e.g. Wanganui Basin, cf. Naish et al. [1998. Quaternary Science Reviews 17 695???710].

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  • Fingerprints and age models for widespread New Zealand tephra marker beds erupted since 30,000 yr ago as a framework for NZ-INTIMATE.

    Lowe, DJ; Shane, Philip; Alloway, Brent; Newnham, R (2008)

    Journal article
    The University of Auckland Library

    The role of tephras in the NZ-INTIMATE project is a critical one because most high-resolution palaeoclimatic records are linked and dated by one or more tephra layers. In this review, first we document eruptive, distributional, and compositional fingerprinting data, both mineralogical and geochemical, for 22 key marker tephras erupted since 30,000 years ago to facilitate their identification and correlation. We include new glass compositional data. The selected marker tephras comprise 10 from Taupo and nine from Okataina volcanoes (rhyolitic), one from Tuhua volcano (peralkaline rhyolitic), and one each from Tongariro and Egmont volcanoes (andesitic). Second, we use four approaches to develop 2??-age models for the tephras (youngest to oldest): (1) calendar ages for Kaharoa and Taupo/Y were obtained by wiggle-matching log-derived tree-ring sequences dated by 14C; (2) Whakaipo/V was dated using an age???depth model from peat; (3) 14 tephras in the montane Kaipo peat sequence (Waimihia/S, Unit K, Whakatane, Tuhua, Mamaku, Rotoma, Opepe/E, Poronui/C, Karapiti/B, Okupata, Konini, Waiohau, Rotorua, Rerewhakaaitu) were dated by simultaneously wiggle-matching stratigraphic position and 51 independent 14C-age points against IntCal04 using Bayesian probability methods via both OxCal and Bpeat; and (4) the five oldest tephras, erupted before ca 18,000 cal. yr BP, were dated by calibrating limited numbers of 14C ages using IntCal04 (Okareka) or comparison curves of the expanded Cariaco Basin sequence (Te Rere, Kawakawa/Oruanui, Poihipi, Okaia). Kawakawa/Oruanui tephra, the most widely distributed marker tephra, was erupted probably ca 27,097??957 cal. yr BP. Potential dating approaches for the older tephras include their identification in Antarctic ice cores (if present) or annually laminated sediments for which robust calendar-age models have been constructed, high-precision AMS 14C dating on appropriate material from environmentally stable sites, systematic luminescence dating, or new radiometric techniques (e.g. U???Th/He) if suitable minerals are available and errors markedly reduced. Further application of Bayesian age-modelling to stratigraphic sequences of 14C ages, possibly augmented with luminescence ages, may help refine age models for pre-Holocene tephras with the largest errors. Finally, we discuss the critical role these marker tephras play in the ongoing construction of an event stratigraphy for the New Zealand region, which is a key objective of Australasian and Southern Hemisphere INTIMATE projects.

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  • Archaeological implications of a widespread 13th Century tephra marker across the central Indonesian Archipelago

    Alloway, Brent; Andreastuti, S; Setiawan, R; Miksic, J; Hua, Q (2017-01-01)

    Journal article
    The University of Auckland Library

    Despite the occurrence of exceptionally large eruptions in the Indonesian Archipelago in recent historic times (i.e. Krakatoa 1883, Tambora 1815), no historic tephra beds have been widely identified in the terrestrial realm that could facilitate the correlation of equivalent aged sequences and/or archaeological remains. This study has identified one such tephra bed of 13th Century age that can be correlated throughout central-east Java and now can be unequivocally correlated with the Samalas 1257 A.D. tephra recently described from Lombok. The occurrence of this historic tephra marker extending ???650 km west from its eruptive source provides the first opportunity to effect inter-regional correlation over large swathes of central Indonesia. It remains entirely conceivable that in the aftermath of this exceptionally large eruptive event there was considerable westward disruption to subsistence agriculture and trade, food shortages and famine, dislocation of affected populations and socio-political unrest on a scale that equalled or exceeded the catastrophic effects documented from the more recent Tambora 1815 A.D. eruption. Indeed the effects of this mid-13th Century eruption can be registered globally in a variety of records from Antarctica, Europe, Middle East and the Americas. Unfortunately, archaeological evidence indicating such disruption in mid-13th Century Indonesia is yet to be deciphered from the so-far sparse accounts and inscriptions of that time. However, this paucity of evidence does not diminish the utility of this widespread tephra bed as a unique chronostratigraphic marker for archaeological studies across large areas of central Indonesia.

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  • Deep???ocean record of major late Cenozoic rhyolitic eruptions from New Zealand

    Carter, L; Alloway, Brent; Shane, P; Westgate, J (2004-09)

    Journal article
    The University of Auckland Library

    A 12 m.y. record of large rhyolitic eruptions from the Coromandel (CVZ) and Taupo (TVZ) Volcanic Zones of New Zealand is contained in cores retrieved by Leg 181 of the Ocean Drilling Program. Site 1124, located 670 km from the TVZ, has a maximum of 134 macroscopic tephra layers with a total thickness of 13.18 m. These units, along with between 7 and 63 tephras from 3 other sites, were dated by a combination of magnetostratigraphy, biostratigraphy, isothermal plateau fission track determinations, and geochemical correlation with onshore tephra deposits. Additional time control for the last 3 m.y. came from an orbitally tuned, benthic, oxygen isotope profile for Site 1123. Results extend the incomplete terrestrial record of volcanism by placing the first major rhyolitic eruption in the CVZ at c. 12 Ma, c. 1.6???1 m.y. earlier than previously known. Tephras became thicker and more frequent from the late Miocene into the Quaternary???a trend that probably reflected (1) more frequent and intense volcanism and (2) reduced distances between sources and depositional sites on the evolving Australian/Pacific plate system. The passage from CVZ to Quaternary TVZ occurred without a major hiatus in activity, suggesting the transition was gradational. The ensuing TVZ volcanism was more continuous than known previously from the onshore geology. Ash dispersal was primarily eastward, highlighting the dominance of westerly winds since the middle Miocene. Nevertheless, variations in dispersal patterns suggest periodic changes in wind direction/speed and/or ejection of ash beyond the Roaring Forties.

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  • Stratigraphy, age and correlation of middle Pleistocene silicic tephras in the Auckland region, New Zealand: A prolific distal record of Taupo Volcanic Zone volcanism

    Alloway, Brent; Westgate, J; Pillans, B; Pearce, N; Newnham, R; Byrami, M; Aarburg, S (2004)

    Journal article
    The University of Auckland Library

    Coastal sections in the Auckland region reveal highly carbonaceous and/or highly weathered clay???dominated cover???bed successions with numerous discrete distal volcanic ash (tephra) layers, fluvially reworked siliciclastic (tephric) deposits, and two widely distributed pyroclastic density current (PDC) deposits generated from explosive silicic volcanism within the Taupo Volcanic Zone (TVZ). The younger of the two PDC deposits (informally named Waiuku tephra) is glass???isothermal plateau fission???track (ITPFT) dated at 1.00 ?? 0.03 Ma and occurs in a normal polarity interval interpreted as the Jaramillo Subchron. Waiuku tephra is correlated with Unit E sourced from the Mangakino Volcanic Centre of the TVZ. Waiuku tephra can be subdivided into two distinctive units enabling unequivocal field correlation: a lower stratified unit (dominantly pyroclastic surge with fall component) and an upper massive to weakly stratified unit (pyroclastic flow). At many sites in south Auckland, Waiuku tephra retains basal ???surge???like??? beds (<1.4 m thickness). This provides clear evidence for primary emplacement and is an exceptional feature considering the c. 200 km this PDC has travelled from its TVZ source area. However, at many other Auckland sites, Waiuku tephra displays transitional sedimentary characteristics indicating lateral transformation from hot, gas???supported flow/surge into water???supported mass flow and hyperconcentrated flow (HCF) deposits. The older PDC deposit is dated at 1.21 ?? 0.09 Ma, is enveloped by tephras that are ITPFT???dated at 1.14 ?? 0.06 Ma (above) and 1.21 ?? 0.06 Ma (below), respectively, and occurs below a short normal polarity interval (Cobb Mountain Subchron) at c. 1.19 Ma. This PDC deposit, correlated with Ongatiti Ignimbrite sourced from the Mangakino Volcanic Centre of TVZ, has laterally transformed from a gas???supported, fine???grained pyroclastic flow deposit at Oruarangi, Port Waikato, into a water???supported volcaniclastic mass flow deposit farther north at Glenbrook Beach. The occurrence of Ongatiti Ignimbrite in Auckland significantly extends its northward distribution. Large numbers of post??? and pre???Ongatiti rhyolitic tephra layers, ranging in age from c. 1.31 to 0.53 Ma, are also recognised in the region, with some up to 0.5 m in compacted fallout thickness. Although some tephras can be attributed to known TVZ eruptions (e.g., Ahuroa/Unit D), many have yet to be identified in proximal source areas and remain uncorrelated. However, some can be reliably correlated to tephra layers occurring in marine to nearshore sequences of Wanganui Basin and deep???sea cores retrieved east of North Island. The identification of previously unrecognised mid???Pleistocene TVZ???sourced tephra deposits in the Auckland region, and their correlation to the offshore marine record, represent an advance in the construction of a higher resolution history for the TVZ where, close to eruptive source, the record is fragmentary and obscured by deep burial, or erosion, or both.

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  • Stratigraphy and chronology of the Stent tephra, a c. 4000 year old distal silicic tephra from Taupo Volcanic Centre, New Zealand

    Alloway, Brent; Lowe, DJ; Chan, Robert; Eden, D; Froggatt, P (1994-03)

    Journal article
    The University of Auckland Library

    Tephrostratigraphic and chronologic studies in two areas of the North Island have identified a previously unrecorded, thin, distal silicic tephra derived from the Taupo Volcanic Centre. In Taranaki, three radiocarbon ages of the uncorrelated tephra are consistent with the independent radiocarbon chronology obtained from enveloping Egmont???sourced tephras. In western Bay of Plenty, where the uncorrelated tephra is also directly dated, it is overlain by Whakaipo Tephra (c. 2.7 ka) and underlain by Hinemaiaia Tephra (c. 4.5 ka). From these sites in Taranaki and western Bay of Plenty, seven radiocarbon dates obtained on the uncorrelated silicic tephra yield an error???weighted mean age of 3970 ??31 conventional radiocarbon years B.P. The ages on the uncorrelated tephra (informally referred to as Stent tephra) from both areas are statistically identical but significantly different from those on both Waimihia and Hinemaiaia Tephras. The occurrence of Stent tephra in Taranaki, c. 160 km upwind from the postulated source area, and in western Bay of Plenty, suggests that it represents the product of a moderately large plinian eruption. Until recently, its validity as a discrete eruptive event had been problematical, because a near???source equivalent deposit between Waimihia and Hinemaiaia Tephras was not recognised in the Taupo area. However, a revised stratigraphy proposed by C. J. N. Wilson in 1993 for eastern sectors of the Taupo area shows that multiple tephra layers were erupted from Taupo volcano between c. 3.9 and 5.2 ka. Of these newly recognised layers, unit???g???the product of a moderately large eruption (???0.15 km3) at c. 4.0 ka???is tentatively correlated with Stent tephra. Other eruptive units recognised by Wilson are either too old or too small in volume to be considered as likely correlatives.

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